Muscle Tissue Flashcards
types of muscle
- skeletal
- cardiac
- smooth
contraction mediated by
thin and thick myofilaments
thin filaments
molecular comp
globular actin monomers (G-actin) > polymers> double helix filamentous actin
troponin complex (3 subunits)
tropomyosin molecule
troponin complex
TnC - bind calcium
TnT- attach tropomyosin
TnI- inhibit actin/myosin interaction, binds troponin complex to actin molecules
tropomyosin molecule
alpha helix of 2 polypeptide chains
each molecule covers 7 G-actin active sites
head to tail assembly of molecules = tropomyosin filament
thick filaments
composition
myosin II (200 molecules)
myosin molecule
components
2 heavy chains + 4 light chains
heavy chain = alpha helix tail w/ globular heads
light chain = small chunks/golf balls on globular heads
trypsin + myosin molecule
trypsin breaks myosin molecule into 2 segments
heavy meromyosin- 4 light chains, 2 globular heads, short twisted tail
light meromyosin- long twisted tail
heavy meromyosin + papain
papain further breaks down heavy
two S1 (2 light chains + 1 head)
one S2 (short twisted tail)
thin + thick filaments
= sarcomere
contracting unit of skeletal/cardiac muscle
cylindrical shape
thin and thick alternate/overlap
myofibril
combo of bands (A/H + I/Z), assembly of sarcomeres
enclosed in skeletal muscle cell (fiber) > fasciculus (bundle)
assembly of sarcromeres
A band
thin and thick
bisected by H band (thick only)
dark and wide
I band
thin only
bisected by Z (attachment for thin filaments)
light
sarcomere accessory proteins
purpose
attach, space, algin myofilaments for even, precise, orderly arrange
alpha actinin
attach thin filaments to Z disk
nebulin
thin filaments to Z disk
2 molecules / 1 thin
nonelastic
titin
thick to Z
elastic so produce tension/force generating
4 titin/ 1 thick
midline proteins
M line
myomesin
C protein
thick to M band (middle of H)
endomysium
skeletal muscle
surrounds each muscle fiber/cell
retiuclar fibers + external lamina
perimysium
skeletal muscle
thin collagenous CT
surround each bundle/fascicle
epimysium
aka deep fascia (dense, irregular collagenous CT)
surrounds gross muscle
nerves and vessels
skeletal muscle
appearance
banding/striated longitudinal
mulitnuclei pushed to periphery- euchromatic, oval shape
uniform size of cells cross section
in LM only see A (dark) and I (light) bands
cardiac muscle
appearance
weak striated/banded but branched so different size (cross sections)
have intercalated discs and capillaries, and atrial granules (hormones inside)
smooth muscle
appearance
spindle shape
1 nucleus in middle
different size cells (cross section)
no striations/sarcomeres
sardines, little extracellular space
skeletal muscle
composition
T tubules- invaginations of sarcolemma, continuous w/ ECS, carry nerve impulses
SR- elaborate sER meshwork surrounding myofibrils
terminal cisternae- part of sER, next to T tubules, store Ca in lumen
triad of skeletal muscle
one T-tububle + two terminal cisternae
motor unit
neuron + all skeletal muscle fibers it innervates
have end plates aka myoneural junction - 1 per/fiber, have axon terminal (Ach) + synaptic cleft + skeletal muscle cell sarcolemma/post synaptic membrane
myasthenia gravis
acetylcholine (Ach)
antibodies attach to receptors so Ach can’t bind = muscle weakness
atrial granules
cardiac muscle
have atrial natriuretic peptide and brain natriuretic factor (diuretics, act on kidneys to lower BP or loss of water/sodium)
most numerous in R atrium fibers
intercalated discs
specialized junctions of cardiac muscle
transverse portion: fascia adherens (transmit contractile forces cell to cell) and desmosomes (bind cells together)
lateral portion: gap junctions, allow ion flow
purkinje fibers
specialized cardiac muscle
like batteries to ignite regular cells to contract
conducting system
@ endocardium (inner most layer heart)
dystrophin
accessorry protein
cytoplasmic
binds thin to laminin (external lamina surrounding fiber)
if absent = muscular dystrophy aka weakness and wasting/ atrophy
caveolae
smooth muscle
pinocytotic vesicles
bubble like on inner surface of cell membrane
release Ca into cell for contraction
myofilament bundles
criss cross to form dense bodies
points of attachment on internal suface of cell membrane to anchor
presynaptic events
- nerve transmitted down axon
- impulse reaches presynaptic membrane
- Ca2+ ions enter terminal
- synaptic vesicles attach to inner surface of presynaptic membrane
- synaptic vesicles release Ach into cleft
start with nerve down axon
end w/ Ach release
postsynaptic events
- Ach binds to receptors on postsynaptic membrane
- Na+ ions enter skeletal muscle cell
- K+ ions exit skeletal muscle cell
- sarcolemma becomes depolarized
- depolarization spreads to T-tubule opening
start Ach binding receptors
end at T-tubules
events inside skeletal muscle cell
- depolarization spreads to T-tubule membrane
- nerve impulse carried deep into muscle cell
- depolarized T-tubule trigger change in permeability of terminal cisternae of SR @ each side of T-tubule
- Calsequestrin from SR releases Ca2+ ions into cytoplasm
- Ca ions attach to TnC of troponin = conformational change
- TnT pushes tropomyosin filaments deeper into groove of actin to uncover active sites
- myosin head associates w/ active site of actin monomer using ATP
- head and rod of myosin bend to pull actin filament over myosin filament = sliding of thin filament towards midline
